1. Field of the Invention
The present invention relates to a field emission cold cathode device of a lateral type, a manufacturing method thereof, and a vacuum micro-device.
2. Description of the Related Art
In recent years, a field emission cold cathode device utilizing Si semiconductor processing techniques has been actively developed. As a typical example of such a device, a field emission cold cathode device of a vertical type described by C. A. Spindt et al in Journal of Applied Physics, Vol. 47, 5248 (1976) is known. This field emission cold cathode device has, on a Si single-crystalline substrate, a conical emitter and a gate electrode disposed to surround the distal end of the emitter.
A field emission cold cathode device of a lateral type (Tech. Digest of IEDM 85, p. 172 (1985)) proposed by R. Green, H. F. Gray et al in view of the problems of the field emission cold cathode device of a vertical type is also known. This field emission cold cathode device has an emitter and gate electrode disposed on one substrate to oppose each other. The field emission cold cathode device of a lateral type is advantageous in that it can be manufactured easily and provide a high yield.
According to the field emission cold cathode device of a lateral type, an emitter end face opposing the gate electrode has, in a direction perpendicular to the substrate surface, a sharpness of about 80 nm to 500 nm corresponding to the emitter thickness, and a sharpness of about 40 nm to 250 nm as the radius of curvature of the distal end. In a direction parallel to the substrate surface, however, this emitter end face is parallel to the gate electrode and has zero sharpness. In other words, the emitter end face opposing the gate electrode does not have a three-dimensional sharpness but only has a two-dimensional sharpness, and has a high driving voltage. This is the disadvantage of this device. When the emitter end face is to be sharpened three-dimensionally, a sharpness exceeding that of the lithography cannot be obtained. Thus, the sharpness usually stays at about 50 nm to 100 nm in a direction parallel to the substrate surface. When the number of precise lithography steps increases, the merit of simplifying the manufacturing method declines.
As a field emission cold cathode device, one using fullerenes or carbon nanotubes to form an emitter is proposed (for example, Jpn. Pat. Appln. KOKAI Publication No. 10-149760). Since the distal ends of the fullerenes or carbon nanotubes have a small radius of curvature, they can decrease the driving voltage and improve the field emission efficiency. Since the fullerenes and carbon nanotubes less depend on the atmosphere and are less influenced by the residual gas, they are expected to operate also at a low vacuum degree.
In the cold cathode device of this type, the emitter can be formed by dispersing fullerenes or carbon nanotubes in an organic solvent, passing the dispersion through a ceramic filter, and bonding the fullerenes or carbon nanotubes on the filter onto a substrate. The emitter can alternatively be formed by depositing fullerenes or carbon nanotubes on a substrate directly by CVD or the like. Furthermore, the emitter can also be formed by dispersing fullerenes or carbon nanotubes in a thick film paste, printing the paste, and sintering the paste at a high temperature (about 500° C. to 800° C.).
With the method of bonding or depositing fullerenes or carbon nanotubes onto a substrate, the emitter is adhered weakly, and is easily separated by a strong field applied to it. With the method of forming fullerenes or carbon nanotubes by printing, the performance may be decreased or degraded by causes such as high-temperature sintering. With both bonding and printing, the resulted carbon nanotubes are not oriented well to an extracting electrode, and the problems of an increase in driving voltage, nonuniform electron emission, and the like exist.
With the bonding method, since carbon has a high chemical resistance and is difficult to etch, it is very difficult to pattern carbon to correspond to the cathode interconnection. With the depositing method in accordance with CVD, a transition-metal catalyst is necessary, and must be very small. This increases the resistance of the interconnection, leading to signal delay or the like. With the printing method, the film has a high resistance, and it is difficult to form a thick film. Therefore, a low-resistance interconnection is difficult to form, and signal delay or the like also tends to occur.
In this manner, as the field emission cold cathode device, various types of devices are proposed, e.g., a lateral one aiming at improvement of the drawbacks of the vertical device, and one using carbon nanotubes or fullerenes to form the emitter. The conventionally proposed field emission cold cathode device is, however, not sufficient in terms of sharpness, driving voltage, reliability, yield, manufacturing easiness, and the like. Under these circumstances, in a field emission cold cathode device of a lateral type and a vacuum micro-device using it, a device structure and a manufacturing method that can achieve a low driving voltage, a high field emission efficiency, and a high integration degree are sought for.